Population Trends

Octopus densities were lowest in 1995 and 2004, while density rose in the intervening years (Fig. 20.1; nonparametric medians test: N = 107, chi-square = 15.537, df = 5, asymptotic sig. = 0.008; Kruskal-Wallace ANOVA: N = 107, chi-square = 11.284, df = 5, asymptotic sig. = 0.046). Overall beach walk densities in 2002 (N = 7, average density = 0.85 per 1,000 m2) were nearly four times those found in 1995 (N = 30, average density = 0.22 per 1,000 m2), and have declined since (Fig. 20.1). An apparent low at the start of the study in 1995, and a subsequent rise and then fall again by 2004 can be found in all Green Island sites taken together (Kruskal-Wallace ANOVA: N = 37, chi-square = 1.897, df = 5, not significant), in

All PWS sites (N=90 octopuses)

EL01 (harvested, N=5)

All Ellamar area (N=18)

1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005

Year of count

Fig. 20.1 Octopus counts over all sites (heavy line) and select individual sites. PWS- Prince William Sound; GR17B, GR17C -Green Island sites; EL01 -harvested Ellamar site. Sampling effort was not equal at each site.

the most frequently sampled Green Island sites taken individually (Fig. 20.1; GR17C and in contrast GR17B), and in all Ellamar areas sites (including Busby Island) taken together (Kruskal-Wallace ANOVA: N = 37, chi-square = 4.152, df = 5, not significant; see Fig. 20.1). Year to year differences at each location did not approach significance due to the lower sample size when the data were subdivided. One site showing a contrasting pattern is the harvested EL01 site (Ellamar), which although low in 1995 shows an apparent decline to near-zero octopus densities in the period 2001-2004. Only one octopus was found (in 2002) on beach walk transects during this period. However, this site is regularly harvested by local residents, who are reported to harvest the beach in the days or months preceding our beach walk transects. Exact harvest rates are not known, but human residency at Ellamar has increased over the decade of this study.

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